The present invention generally relates to medical electrical stimulation, and more particularly, to a lead system for providing medical electrical stimulation to either two locations in a single atrium or to a site in each of the two atria of a patient""s heart.
Electrical stimulation of body tissues and organs is often used as a method of treating various pathological conditions. Such stimulation generally entails making electrical contact between body tissue and an electrical pulse generator through one or more stimulation leads. Various lead structures and various techniques for implanting these lead structures into body tissue and particularly the heart have been developed. For example, a transvenous endocardial lead is passed through a vein, with the assistance of a fluoroscope, into the heart where it may be held in electrical contact with the endocardium of the right atrium or ventricle.
The left chambers of the heart are presently not available for the implantation of long term transvenous leads due to risk of thrombus or clot formation. In particular, blood flows through the right side of the heart, through the lungs, through the left side of the heart and then through the rest of the body, including the brain, before returning again to the right side of the heart. Implanted objects often cause minor blood clots and thrombus to form in the blood. These may, on occasion, dislodge and be released into the bloodstream. Because the blood circulates directly from the left atrium and ventricle to the brain, any clots could have serious consequences if they were to reach the brain, e.g. a stroke. In contrast, any clots released from an object implanted in the right side of the heart would simply travel to the lungs, where they would lodge without any serious risk. Thus at present, chronic transvenous leads may not be safely implanted within the left side of the heart.
In spite of the difficulties, there remains a great need to be able to electrically stimulate the left side of the heart. As a result, transvenous lead placement into the coronary sinus (CS) or deeper into the great cardiac vein (GCV) or other coronary vein has recently become an important technique for cardiac pacing and defibrillation electrode implantation to gain electrical access to the left side of the heart. U.S. Pat. No. 4,932,407 to Williams; U.S. Pat. No. 5,099,838 to Bardy; and U.S. Pat. Nos. 5,348,021; 5,433,729; and 5,350,404 to Adams et al., incorporated herein by reference, describe inserting a lead through the right atrium and CS into one of the coronary veins. To implant a lead made in conformance with the present invention, the implanter passes the lead through a guide catheter, or introducer, until it is in or near the CS. This is done using a standard technique of stiffening the lead with a stylet, guiding the stiffened lead by hand through the right atrium (RA) and into or near the CS, aided by fluoroscopy. Following proper placement, any stiffening stylets or guide catheters are retracted.
As an example of placing leads into the CS, dual site right atrial pacing and biatrial pacing with the left atrium paced from the CS are being studied to reduce the incidence of paroxysms of atrial fibrillation. In a recent publication (Daubert et al., xe2x80x9cBiatrial Synchronous Pacing: A New Approach to Prevent Arrhythmias in Patients with Atrial Conduction Block,xe2x80x9d from Prevention of Tachyarrhythmias with Cardiac Pacing, Futura Publishing Company, Inc., Armonk, N.Y., 1997, p. 111), dual site pacing has been done by pacing the RA cathodically and the LA anodically, using a Y adaptor. This composite dual atrial lead configuration detects three successive intracardiac signals: the RA electrogram, the LA electrogram, and a far field R wave sensed in the CS and corresponding to LV depolarization. If the pacemaker misinterprets these LV signals as originating in the atria, inappropriate inhibition or inappropriate triggering may occur, possibly creating a pacemaker-mediated tachycardia (PMT). In U.S. Pat. No. 5,514,161 to Limousin, a Y adaptor is used as described above, and software is used to deal with the ventricular signals in order to avoid such a PMT. It would be desirable to provide dual site pacing without requiring a Y adaptor or added connectors, and sensing only one atrial bipolar signal while rejecting ventricular signals.
As another example of placing leads into the CS or deeper, defibrillation electrodes within the CS have been shown to reduce atrial and ventricular defibrillation thresholds. U.S. Pat. No. 5,476,498 to Ayers shows an example of a lead having an atrial defibrillation electrode for implantation within the CS.
As yet another example of placing leads through the CS and deeper into a coronary vein, pacing the left ventricle (LO from within a coronary vein appears to improve hemodynamics in certain disease states such as heart failure. For example, in patients with dilated cardiomyopathy, electrical stimulation of both the right side and the left side of the heart has been shown to be of major importance to improve the patient""s well-being and manage heart failure. See, for example, Cazeau et al., xe2x80x9cTour Chamber Pacing in Dilated Cardiomyopathy.xe2x80x9d PACE, November 1994, pp. 1974-79.
The functions desired of pacemakers and pacemaker/defibrillators currently require a large number of electrodes, a large number of lead connectors, and a large header with a large number of connector cavities. A solution is needed to provide needed features while not increasing device size and hardware to a clinically unacceptable level, and while still using standard (IS-1 and DF-1) connectors.
It is therefore an object of this invention to provide a lead or lead system that paces two sites simultaneously while sensing from essentially only one.
It is a further object of this invention to provide a lead or lead system that uses standard connectors.
It is a further object of this invention to reduce the hardware required without a reduction in desired features.
It is a further object of this invention to provide a lead system that does not require any adaptors.
It is a further object of this invention to provide a lead system for which no extra switches are required for switching between electrodes for pacing and sensing.
Briefly, the above and further objects and features of the present invention are realized by providing a system that uses one connector for both dual site pacing and single site sensing. In a first embodiment of the invention, the first pacing site is an RA location, and the second site is a second RA site near the CS os. In an alternative embodiment, the second site is an LA site through the CS. In one embodiment, a CS (LA) pacing electrode at the second site is electrically coupled to an RA electrode at the first site, with each acting as the cathode in its respective chamber. The anode for both is a second RA electrode, which may be either a dedicated ring electrode or a defibrillation electrode.
The present invention may include a CS defibrillation electrode, and the second site pacing electrode may be located either proximal or distal of the CS defibrillation electrode. If located distal of the CS defibrillation electrode, the electrode paces the LA; if proximal, the electrode may be positioned to pace the LA or a second site in the RA.
In the preferred embodiment, the lead is preshaped to encourage contact of the electrodes with the endocardium. For example, a curve in the portion of the lead to be positioned in the RA may be used to force the RA electrodes in contact with the RA endocardium. Likewise, one or more angles on the distal end of the CS lead may be used to force the LA electrode in contact with the CS oriented toward the LA. See for example U.S. Pat. No. 5,683,445 to Swoyer, which is incorporated herein by reference.
By keeping the LA (CS) pacing electrode very small, its current density can be kept high for pacing, while getting very little sensed signal from it (compared with the RA electrode). Increasing the impedance of the LA electrode as compared with the RA electrodes will accomplish this. Besides keeping the macroscopic surface area small, the microscopic surface area should also be kept small. In one embodiment of the invention, a smooth platinum or platinum iridium alloy tip is used to accomplish this in a lead that is stable within the CS in which sensing is not desirable. The RA electrodes are preferably porous to optimize sensing. In an alternative embodiment, one of the RA electrodes is replaced by an RA/SVC defibrillation electrode.